The focus, of course, is on getting as warm as possible after the plunge.

"We have everything ready," said Sirkka Wakefield of Cotuit, who will be taking the plunge at Loop Beach in Cotuit with her husband, Tim.

Bathrobes will be waiting on the beach and socks or slippers warming in the car, she said.

No ties, snaps or buttons are allowed — the Wakefields' fingers will be too numb to manipulate tiny clothing devices, she said.

She has participated in the Polar Bear Club's annual New Year's Day Swim every year for the past five years.

The worst part is the feeling of "pins and needles on your feet," Wakefield said. Next is the "instant brain freeze" that occurs when plungers dunk their heads, she said.

Karen Marciante, director of the Yarmouth Senior Center, compared the shock of jumping into the water at Bass River Beach in South Yarmouth to being Tasered.

At least that's how several police officers have described the sensation of participating in the Annual Polar Plunge for Yarmouth Seniors, she said.

"I've never been Tasered," Marciante said.

But she's done the plunge since its inception two years ago and plans to do it again New Year's Day.

The key is to psyche yourself up and get it over with, Marciante said. "The anticipation is worse than the actual event. You can't go slow. It's got to be quick."

It's against the plungers' code of honor to wear wetsuits or drysuits, but many pull on sneakers to cope with the fact that their feet almost immediately go numb in 30- to 40-degree water temperatures, Marciante said.

Immersion in cold water causes blood vessels to constrict, Dr. Alan Steinman of Olympia, Wash., an expert on hypothermia, said.

This helps the body to retain heat and prevent it from leaving through the skin, he said.

Steinman, who retired from the Coast Guard as a rear admiral, knows it's painful because he's immersed himself in cold water to encourage study subjects in hypothermia to stay put.

The message was, "If I can do it, you guys can do it, too," Steinman said in a phone interview.

The good news is polar plungers have almost zero risk of hypothermia, Steinman said.

It takes about 30 minutes for the body's core temperature to drop to hypothermic levels in water of 50 degrees or less, he said. And polar bear plungers don't stick around that long, Marciante said. "It's a turnaround," she said. "You run in, dunk and then you're out."

The plunges are harmless for most people but should be avoided by those with high blood pressure or cardiac issues, Steinman said.

Participants experience a "cold shock reflex" that causes blood pressure and heart and breathing rates to temporarily spike — not a good idea in those at risk of stroke or heart attack, he said.

Marciante said she cleared the polar bear plunge with her doctor.

"He just said, 'It's fine,'" she said, but she thought she also detected a look of "Why would you even want to do this?"

Polar bear plungers use the word "fun" a lot, to the bewilderment of family and friends.

"It's for fun and to raise money" for charity, Wakefield said. This year's Cotuit event benefits the family of Chris VanGelder, a Mashpee resident and father of three who was in a motorcycle accident.

Yarmouth Police Chief Frank G. Frederickson talked a lot about the good times associated with his five polar bear plunges, even though one year's dunk in Barnstable Harbor was shared with floating chunks of ice.

"It's full of excitement," said Frederickson, who will be at Bass River Beach on New Year's Day. He said that growing up, members of South Boston's

L Street Brownies — one of the oldest polar bear clubs in the country — were a legend.

"It's cheap thrills," Frederickson said. "It feels great once you get out."

Noon Tuesday; Polar plunge for pancreatic cancer research in memory of Doug Isenhour, who died in 2011; at Surrey Lane Beach at Fresh Pond in Falmouth. Donations accepted. Organizer is Amanda Jones of Cotuit Road in Mashpee.

3 p.m. Tuesday, 4th annual New Year's Day Plunge at Millway Beach in Barnstable Village; this year will benefit family of Chhewang Lama of Barnstable, who is seriously ill. Donations accepted and T-shirts will be sold. Organizers are Richards French and Ed Robinson of Barnstable. Swim will be followed by refreshments at Dolphin Restaurant.